Process of tanning hides with a condensation product of an acid salt of a phenyl amine, an acid salt of a lower alkyl amine and paraformaldehyde



IC V Patented Oct. 4, 1960 l 2 4 r p dehyde, especially paraformaldehyde and acetaldehyde.

2,955,012 The invention is further illustratedrby the following ex- PROCESS OF TANNING HIDE'S WITH A CONDEN- SATION PRODUCT OF AN ACID SALT OF A PHENYL AMINE, AN ACID SALT OF A LOWER ALKYL AMINE AND PARAFORMALDEHYDE Adolf Kiintzel and Kurt Rosenbusch, Darmstadt, Germany, assignors to Farbenfabriken Bayer Aktiengesellshaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed July 28, 1954, Ser. No. 446,384

Claims. priority, application Germany July 30, 1953 5 Claims. (Cl. 894.24)

The present invention relates to water-soluble condensation products and to processes for their production.

Tanning agents of vegetable origin are known to be anion-active and also most synthetic tanning agents have anionic character due to their content of phenolic or sulfonic acid groups. Recently, cationic tanning agents of amphoteric character have become known (see for instance US. patent application Ser. No. 241,693, filed August 13, 1951, and now abandoned), which consist of aromatic condensation products containing hydroxy and additionally basic amino groups. These basic groups render the condensation products soluble in acid but they are not responsible for the tanning properties of the aromatic condensation products.

It is an object of this invention to provide novel cationic tanning agents.

A further object is the provision of cationic tanning agents having the capacity of tanning hides directly without any pretanning step being necessary.

Another object consists in the provision of a process for producing tanning agents having the above characteristics. A still further object consists in a process of tanning with the above tanning agents.

Still further objects will become apparent as the following specification proceeds.

In accordance with this invention it has been found that water-soluble condensation products suitable for tanning can be obtained by melting'mixtures of salts of aromatic amines and salts of aliphatic amines with lower aliphatic aldehydes having at most two carbon atoms. These tanning agents which contain no phenolic groups, can be regarded as cationic.

The cationic tanning agents of the present invention differ from the known exclusively aliphatic condensation products which can only be used for the aftertreatment of pretanned hides. The tanning action of the cationic tanning agents of the invention is similar to amphoteric tanning agents; like chrome tanning agents, they are applied by pretanning therewith a pickled pelt in acid solution and efiecting finish tanning by gradually neutralizing the tanning solution.

The character of the leather treated with the tanning agents of the invention can be influenced by neutralizing the tanning agents to a pH value near the neutral point, which gives a very firm leather of light color while a softer and yellower leather is obtained by stopping the tanning process in a weakly acid medium.

The cationic tanning agents of the invention are prepared by melting together salts of aromatic and aliphatic amines with lower aliphatic aldehydes. Examples of aromatic amines are aniline, the toluidines and xylidines; suitable aliphatic amines are especially ethanolamine or diethanolamine, but also aliphatic amines containing no hydroxyl groups, for instance dirnethylamine and like alkylamines, are useful. Furthermore, dicyanodiamidine can be employed in the form of its hydrochloride. Suitable aldehydes according to the invention are formalamples Without being restricted thereto, the parts given being by weight:

Example 1 13 parts of aniline hydrochloride and 10 parts of ethanolamine hydrochloride are heated to 150 C. to form a homogeneous melt. Heating is then stopped and paraformaldehyde is slowly introduced into the melt with stirring; care has to be taken that the addition is carried out so that the temperature does not exceed 140 C. The melt turns into a homogeneous dark red mass which almost solidifies on cooling, easily dissolves in water and has a pronounced capacity for precipitating gelatine. Upon neutralizing the aqueous solution by addition of alkali metal hydroxide solution a white precipitate forms which is insoluble in an excess quantity of the alkali metal hydroxide solution, but can be redissolved by means of acid. The tanning agent can be separated in the form of a yellow precipitate by means of a concentrated common salt solution,

Products with similar properties can be obtained by the use of 14.1 parts of diethanolamine hydrochloride,

14 parts of dicyandiamidine hydrochloride or 8.1 parts of dimethylamine hydrochloride instead of the ethanolamine hydrochloride.

Example 2 14.3 parts of 0-, mor p-toluidine hydrochloride or a mixture of the three isomers are mixed with 10 parts of ethanol amine hydrochloride and 3 parts of paraformaldehyde at 140 C. The brick-red melt easily dissolves in waterif necessary with the addition of a small quantity of acidand has a marked capacity for precipitating gelatine. The tanning agent precipitates from the aqueous solution with a yellowish color by addition of concentrated common salt solution or by neutralizing with an alkali metal hydroxide solution.

If p-toluidine hydrochloride alone is condensed in the above described manner the red melt crystallized on cooling. By pouring the melt into a large quantity of water, colorless felted needles precipitate which can be recrystallized from ethanol and melt at 136 C.

Example 3 13 grams of aniline hydrochloride and 8.1 parts of dimethyl amine hydrochloride are heated to C. to form a homogeneous melt. 14.6 grams of chloral hydrate are slowly introduced into the melt; care has to be taken that the addition is carried out so that the temperature does not exceed C. The brown-red resin easily dissolves in water and is precipitated from tht solution in blue-grey fiakes by addition of alkali metal hydroxide solution. The precipitate can be redissolved by means of dilute acids but is insoluble in an excess quantity of alkali metal hydroxide solution. The resin dissolved in dilute hydrochloric acid contains free primary amino groups of aromatic origin. This is seen by the formation of an intensely red dyestufi upon addition of nitrous acid and alkaline S-naphtol solution.

We claim:

1. A process of tanning hides which comprises pretanning the hides with an acid solution of a cationic tanning agent, said tanning agent being the condensation product obtained by melting at a temperature of about 140 C. stoichiometric amounts of an acid salt of a phenyl amine from the group consisting of aniline and lower alkyl substituted aniline, an acid salt of an amine from the group consisting of lower alkyl amine, hydroxy lower alkyl amine and dicyanodiamidine, and paraformaldehyde, and precipitating the condensation product from the melt, the amino group of the phenyl amine reniainingdree'in tl=ie""'e6i1dnsation product; and effecting finish tanning by gradually "neutralizing said tanning solution. a

2. The process of claim 1, wherein said condensation -pfodufet is prepa'red rremq arr acid salt of aniline, ---an ae-id sale of etlia'rrolan'ii'ne, aiid pa'raforinaldeh'yde.

'3. The"' 'pr'ocess of clairn -l, wherein said condensation product is prepared from an acid salt of anilinejan acid salt of diethanolamine; arid par aformaldehyde.

4. The process of claim 1, whereinsaid condensation product is prepared from an acid salt of aniline, an acid salt oi paratoluidine, and-paraformaldehyde.

5. The process of claim 1, wherein said condensation product is prepared from an acid salt of aniline, an

References Cited in the file of this patent UNITED STATES iPATENTS Petersen Sept. 9, 1940 Grimmy Sept. 7, I943 'DAlelio Nov. 16, 1943 -Gundel Jan. 4, 1944 Olpin et a1. July.5, 1949 'Ran'i'oridt Jan. 15, 1952 Nagy '-Dec.- "9, 1952 

1. A PROCESS OF TANNING HIDES WHICH COMPRISES PRETANNING THE HIDES WITH AN ACID SOLUTION OA A CATIONIC TANNING AGENT, SAID TANNING AGENT BEING THE CONDENSATION PRODUCT OBTAINED BY MELTING AT A TEMPERATURE OF ABOUT 140*C. STOICHIOMETRIC AMOUNTS OF AN ACID SALT OF A PHENYL AMINE FROM THE GROUP CONSISTING OF ANILINE AND LOWER ALKYL SUBSTITUTED ANILINE, AN ACID SALT OF AN AMINE FROM THE GROUP CONSISTING OF LOWER ALKYL AMINE, HYDROXY FLOWER ALKYL AMINE AND DICYANODIAMIDINE, AND PARAFORMALDEHYDE, AND PRECIPITATING THE CONDENSATION PRODUCT FROM THE MELT, THE AMINO GROUP OF THE PHENYL AMINE REMAINING FREE IN THE CONDENSATION PRODUCT, AND EFFECTING FINISH TANNING BY GRADUALLY NEUTRALIZING SAID TANNING SOLUTION. 